Skip to Content

Male vs. Female Sea Monkeys (Key Differences to Know)

Male vs. Female Sea Monkeys (Key Differences to Know)
The purpose of this blog is to share general information and is written to the author's best knowledge. It is not intended to be used in place of veterinary advice. For health concerns, please seek proper veterinary care. In addition, as an Amazon Associate I earn from qualifying purchases.

Sea monkeys are fascinating creatures and make excellent low-maintenance pets. If kept in optimal conditions, these tiny shrimp will continue to reproduce and reward you with years of wriggly activity.

As small as they are, you may be surprised to know that there are distinct differences between male and female sea monkeys.

Male sea monkeys are shorter and smaller than females. Females feature a circular-shaped egg sack on the midpoint of their abdomen, regardless of whether eggs are present. Males have tubular-shaped penes visible on the thorax section. They also have modified longer antenna than females.

Sea monkeys are pretty tiny, so if you haven’t been able to identify which are males or females in your tank, you probably just need a strong magnifying glass. We have made a list of features you should look for to identify the gender of individual sea monkeys easily.

Male vs. Female Sea Monkeys

Sea Monkeys became hugely popular in the 60s and 70s as a result of somewhat overstated marketing, mostly in comic books. Sea monkey families were depicted as aquatic, humanoid-looking creatures with definite male and female characteristics.

Generations of children were universally disappointed to find that instead of the magical eggs hatching out minute naked semi-humans, the result was small shrimp. And on top of that, they were so tiny you needed a magnified viewing portal to see the creatures swimming by clearly.

But once you have come to understand that sea monkeys are simply modified brine shrimp, they can provide hours of entertainment. Learning more about your troop of sea monkeys will lead to greater understanding and enjoyment of these tiny pets.

Let’s discuss how you can distinguish between a male and a female sea monkey. To start with, let’s put all the visible physically differences down on a table:

Male Sea MonkeysFemale Sea Monkeys
Slightly smallerSlightly bigger
It may be shorter in lengthIt may be slightly longer in length
No egg sack presentVisible egg sack around the abdomen area
Tubular Shaped penes may be visible on the thorax – may resemble whiskersNo structures on the thorax
The second set of antennae are elongatedBoth sets of antennae are similar
They may be observed fighting esp if there are many males in a tankFemale sea monkeys do not fight

From this list, it may seem that the differences between the two sexes should be unmistakable. The challenge with easy identification is because of the creatures’ very tiny size and perpetual motion.

Fully grown sea monkeys only reach around a ½ to ¾ inch in length, so be prepared to spend some time observing your tank before you start recognizing some of these tiny detail.

Let’s go through each of the physical differences in a little more detail:

1 – Male Sea Monkeys Are Smaller Than Females

A good place to start when identifying male or female sea monkeys is to look at their size. The ones that seem more robust and bigger are usually the females.

The growth rate of both sexes of sea monkeys is pretty similar until they reach maturity. The females continue to grow a little more after the males have stopped.

It isn’t easy to notice many disenable differences between males and females before they become fully developed adults, between 6 – 8 weeks of age.

2 – Male Sea Monkeys Are Shorter Than Females

Female sea monkeys are generally sturdier and more impressive specimens in your tank. This is also because they are usually significantly longer than the males.

When fully grown, female sea monkeys often get close to ¾ inch in length while most males struggle to reach ½ an inch. To give all your sea monkeys the best chance of reaching their full size, be sure to provide correct light, plenty of oxygen in the water, food, and keep their water at the proper brine concentration.

3 – Adult Female Sea Monkeys Have a Visible Egg Sac

If you look really closely, you will see that some of the bigger sea monkeys in your tank, which we have identified as females, have circular-shaped sacks near the middle of their bodies. At times they will be white or transparent, which is when there is no eggs present.

However, in the right conditions, Sea Monkeys are prolific breeders, and if you keep checking, you are sure to see soon that the sack on some females appears brownish or yellow. This would indicate that there are eggs present, and your sea monkey tank will soon be blessed with some new life.

Sea monkey females usually produce about 20 eggs at a time. Even if she dies while carrying the eggs, they will still be released and hatch.

If you spot a large sea monkey without the female’s distinctive round egg sack attached to its abdomen, you may have a larger than usual male in the tank. Check its antennae for more clues regarding its sex.

4 – Male Sea Monkeys Have Many Tubular Penes

Multiple penes are present on the thorax section of male sea monkey bodies. These tubular structures can be tricky to see when retracted but become 4 x longer when extended.

So if you do not see an egg sac on the abdomen of a sea monkey but instead can see something that looks like tiny tubes in the area above the middle, the sea monkey you are looking at is a male. Some articles describe the penes as sea monkey’ whiskers’.


5 – Male and Female Sea Monkey Antennae Are Different

Besides the size difference, the next most obvious difference that will help you tell the male and female sea monkeys in your tank apart is the differently shaped antennas. Male and females have two sets of antenna structures on top of their heads, but the second set is far more prominent on males.

The size difference of the antennae is to make it possible to clasp onto the females during mating. They are also sometimes called antlers or claspers.

6 – Male Sea Monkeys May Challenge Each Other

If you see two sea monkeys attached, it is in all likelihood a male and a female. They can swim around connected to each other for several days.

However, you may also notice some other close interactions in your tank, especially if you have a lot of sea monkeys. Male sea monkeys sometimes fight for the attention of females.

It is recommended that if you have more than 25 sea monkeys in your tank, you create another tank and move some over to prevent conflict between males.

Final Thoughts

Male and female sea monkeys differ significantly in appearance. The main limiting factor to observing all the differences is their tiny size.

Female sea monkeys are usually slightly bigger and have a noticeable egg sack on their abdomen. Male sea monkeys have larger antennae on their heads and beard-like whiskers on the thorax.